Unstable solar lentigo mimicking lentigo maligna melanoma: A case report

Abstract

Solar lentigo (SL) is a hyperpigmented macule that develops due to chronic ultraviolet exposure. A 35-year-old housewife, presented with an asymptomatic pigmented patch on the right side of her nose for the last 10 years, with a rapid increase in size and variability in pigmentation over the last 3 years. She had no history of excessive sun exposure. Upon examination, there was a solitary, hyperpigmented, well to ill-defined patch of irregular shape and margin, measuring 3 cm * 2.5 cm, with variability in colour and areas of regression, almost covering Right side of nose. The patch appeared light brown with areas of dark brown and black. Differential diagnoses considered were Lentigo maligna melanoma (LMM), Solar Lentigo (SL), and flat seborrheic keratosis. Dermoscopy (Polarised illuco IDS-1100 dermoscope) revealed diffuse brown pigmentation with a faint pigmented network, along with dark brown to black globules and blotches. Due to the asymmetry of pigmentation, a punch biopsy was performed from the area of darkest pigmentation to rule out LMM. In Histology, the epidermis exhibited hyperkeratosis, follicular plugging, acanthosis, and downward elongation of the rete ridges. There was hyperpigmentation of the basal layer, an increased number of melanocytes, and the presence of melanophages in the papillary dermis. The biopsy report was consistent with Solar Lentigo (SL), and we concluded it as unstable solar lentigo (USL). This case is presented due to its clinical and dermoscopic resemblance to LMM and to increase awareness of USL and the importance of periodic surveillance.